1. Technical Field
The present disclosure relates to an electrode strip and a sensor strip, and more particularly, to an electrode strip and a sensor strip having two reactive areas. Notably, the sample liquids accommodated in one reactive area do not contaminate the sample liquids accommodated in the other reactive area.
2. Background
Electrodes made by utilizing electrochemical methods can be divided into two types: enzymatic electrodes and non-enzymatic electrodes. At the present time, the majority of electrodes mentioned in technical literature and used in biological substance measuring are enzymatic electrodes, such as well-commercialized blood sugar electrodes. In regard to non-enzymatic electrodes, most of them are used in the testing of general chemical compounds, such as pH electrodes for testing hydrogen ions. Since many enzymatic electrodes have restrictive conditions for moisture preservation, complicated manufacturing processes, and over-elaborate control conditions, manufacturing costs are quite high and mass production is not feasible, and thus, they are only suitable for use by technicians in research organizations and large scale medical testing units.
Relating to the prior art of non-enzymatic electrode strips, such as an electric current non-enzymatic electrode strip disclosed in U.S. Pat. No. 6,258,230 B1, the manufacturing process uses screen printing to spread the reaction layer formulation to cover two electrode systems. The composition of the reaction layer formulation requires large amounts of polymers mixed with a salt buffer. However, the analyte concentration, measured by the above-identified non-enzymatic electrode strips, is usually interfered by variant hematocrit factors in the blood samples.
The electrochemical method is one of the typical methods for measuring analyte concentration and involves amperometric responses indicative of the concentration of the analyte. An important limitation of electrochemical methods of measuring the concentration of the analyte in blood is the effect of confounding variables on the diffusion of analyte and the various active ingredients of the reagent. Moreover, the electrochemical method has a problem in that the accuracy of the analyte concentration is interfered by hematocrit concentrations (a ratio of the volume of packed red blood cells to the total blood volume).
The normal hematocrit range for an average human being is about 35% to 45%, though in extreme cases, the hematocrit may range from about 20% to about 70%. The mean hematocrit range for a neonatal infant is about 53% to 69%.
Variations in a volume of red blood cells within blood can cause variations in glucose readings measured by electrochemical sensor strips. Typically, a negative bias (i.e., lower calculated analyte concentration) is observed at high hematocrit levels, while a positive bias (i.e., higher calculated analyte concentration) is observed at low hematocrit levels. At high hematocrit levels, the red blood cells may impede the reaction of enzymes and electrochemical mediators, reduce the rate of chemistry dissolution, since there less plasma volume to solvate the chemical reactants, and slow diffusion of the mediator, causing a slower current result. Conversely, at low hematocrit levels, a higher measured current can result. In addition, the blood sample resistance is also hematocrit dependent, which can affect voltage and/or current measurements.
Additionally, the variation of hematocrit levels is extremely broad, and therefore, needs to be measured by a biosensor and biosensor strips. It is highly crucial to design biosensor strips and a biosensor which effectively prevent hematocrit from interfering. How to make a system and a method to prevent hematocrit from interfering with an analyte measurement is needed by the present related manufactory.
U.S. Pat. No. 7,407,811 ('811) described a method for measuring the analyte concentration. The method utilizes an alternative current (AC) excitation to measure hematocrit for correcting the analyte concentration and reducing hematocrit from interfering. Further, the method of '811 is the measuring phase angle and admittance magnitude of the AC excitation and cooperated with a formula to detect hematocrit. '811 further described the blood glucose measurement for correcting hematocrit by using the above hematocrit measurement method, which applies DC and AC signals in only one electrode set and only one reaction zone of a biosensor strip, whether applying AC or DC signal firstly. The phase angle and admittance magnitude of AC excitation is utilized to detect hematocrit, while DC excitation is utilized to detect analyte concentration. Furthermore, parameters of a set formula of the prior method further include temperature, and therefore, the analyte concentration will be corrected with the phase angle, admittance magnitude and temperature. Additionally, the provided AC excitation uses at least two frequencies and may use two to five frequencies in practice, and therefore, the hematocrit is detected by the applied AC excitation using different frequencies.
The method of '811 provides AC and DC signals to a sample in the same reaction zone and further uses only one electrode set for detection, and consequentially, there could be noise produced which would interfere with each other. In addition, a result of uncorrected analyte concentration and hematocrit measured by the provided AC with DC offset to the same reaction zone will interfere with each other's result and then influence the accuracy. The method of '811 further needs the appropriate temperature and two to five AC frequencies to correct the measured analyte concentration, which requires complex operations and an extended amount of time. Furthermore, the cost and complexity of the meter increases as the number of measurements and frequencies increase. Thus, an effective system and method are needed in order to solve the foregoing problem.
U.S. Pat. No. 5,264,103 ('103) describes a biosensor including two electrode sets which are disposed in two separated reactive areas, respectively. Two electrode sets are disposed on two sides of a single substrate. Although the substrate separates one electrode set from the other electrode set, two electrode sets might be easily interfered by each other due to adjacency between the upper electrode set and the lower electrode set. For instance, when the upper electrode set is applied with an AC signal for measuring hematocrit levels, a response signal in the lower electrode set will be induced in response to the AC signal of the upper electrode set due to the electrical coupling and as a result, the DC signal applied to the lower electrode will be interfered. Thus, the design of '103 cannot perform a simultaneous measurement in the upper electrode of the first reactive area and the lower electrode of the second reactive area. In addition, the biosensor strip of '103 includes two vent holes disposed on two opposite sides of the substrate. However, if the amount of sample liquid exceeds the capacity of the biosensor strip, the sample liquids may overflow the vent hole and cause contamination. Furthermore, if two electrode sets are disposed on two opposite sides of the substrate, the substrate with a printed electrode set has to be upside down for printing the other electrode set on the substrate in the manufacturing process. Since the substrate with the two electrode sets is placed on a friction surface, the electrode set printed on the lower surface of the substrate is easily abraded in the manufacturing process.
In addition, many electrochemical biosensor strips sold on the market have another problem in that a sample volume will also influence the accuracy. In the measurement of blood glucose, for example, it is quite sensitive to blood sample volume, and if the sample is insufficient, then that will cause an error in the calculation. Thus, an effective system and method are needed in order to solve the above disadvantage.